The present disclosure is related to an arrangement and a method for annulus volume integrity monitoring. More specifically the present disclosure relates to an arrangement and method for determination of annulus free volume of a flexible riser. The monitoring can be performed by use of a logical unit which runs the annulus testing with diffusion or gas feed.
Monitoring and integrity evaluation are performed to control and map the condition and quality of the annulus volume in as an example a pipe, typically a flexible riser. Annulus testing for calculation of annulus free volume is a significant part of the pipe integrity evaluation. As shown in FIG. 1, the annulus volume 102 in a flexible pipe is defined as the area between the outer sheath 101 and the pressure barrier 103.
Based on such an annulus test, the fluid content in annulus can be evaluated by comparing the measured annulus free volume and knowledge of the total annulus volume. The annulus volume in a flexible pipe is expected to remain dry or experience a slow filling during time due to among other factors diffusion through the pipe pressure barrier. Annulus testing of flexible risers is per today typically performed annually at offshore installations in the Norwegian continental shelf. FIG. 2 shows an example sketch of an offshore installation which comprises a flexible pipe 201, a platform 202 and a test location 203. The annulus testing of the flexible pipe 201 is typically performed at test location 203.
Results from manual annulus tests are typically input for calculation of the pipe's remaining lifetime. As an example the annulus volume can be fluid filled due to damaged outer sheath. The deterioration and therefore the remaining pipe lifetime with fluid filled annulus, is typically calculated based on the time of execution of the latest annulus test. If latest test was performed one year ago, one year of the remaining lifetime must be subtracted, by assuming that the damage appeared shortly after the previous test. Large expenses are therefore likely to occur by not being able to operate the pipe up to one more year or due to short time for planning when a flexible pipe needs to be replaced. The long time intervals between each annulus test is therefore a problem today. Especially some pipes require tight follow-up.
At present, annulus testing is performed manually, which requires key personal offshore to perform the testing. Thus the testing is dependent on human variations and factors, which can result in tests not being performed or not to be performed when scheduled. Additionally, human factors can cause separate parameter basis for separate tests. It can also be mentioned that for some pipes ventilating of annulus is performed directly in to the open, which cause danger for corrosion due to oxygen access.